Dolby Atmos Music is mixed so that instruments or vocal tracks (called objects) sound like they're appearing in different parts of a room. For instance, you might hear the vocals coming from the front, while the other instruments are coming from all around you. That means "listeners can discover hidden details and subtleties with unparalleled clarity," according to Dolby. The encoding works regardless of how many speakers you have.
If you're a Tidal HiFi subscriber, the app will default to the Dolby Atmos experience if its available on a track. "Tracks will be identified by a 'Dolby logo' visual badge as well as through a 'Dolby Atmos' identifier that will display once a song is selected," according to the press release. You can also scroll through a list of Dolby Atmos tracks under the Explore tab. Tidal said that it's also "working closely with its artist-owners, including Jay-Z, to mix their catalogs in Dolby Atmos -- which are expected to become available in 2020."